Since Hounsfield invented the first CT machine in 1972, the CT technology brings out outstanding affect in medical diagnosis and industrial lossless detection. The CT technology now becomes one of the important detection means in various industries such as medicine, biology, aviation, national defense, etc. As the technology develops, the CT scanning and imaging improves increasingly, and the three-dimensional cone beam CT becomes the object of research and application. X-ray cone beam CT is applicable in various fields such as medical clinic, security inspection, lossless detection, etc. The CT becomes an indispensable detection means in the medical clinic.
The spiral CT is applied to the medical clinic since 1989. It gradually replaces the conventional CT technologies due to its prominent advantages. The advantage of the spiral CT over the conventional CT is that the spiral CT can collect projected data continuously without any interruption, and can obtain the three-dimensional body data of an object by means of a specially designed reconstruction algorithm, thereby the time required for CT scanning is reduced greatly, a Z-axis resolution of the reconstructed image can be provided, and the false track of movement can be reduced. The spiral CT is successful in the clinic application, and thus the detector used in the spiral CT develops from a single slice to 2 slices, 4 slices, 8 slices, 16 slices, and to 32 slices, 64 slices or even 128 slices. A spiral CT of 320 slices was released the first time by Toshiba Company in 2007. Another technology, i.e., a panel detector technology, improves as the spiral CT progresses. The multi-slice spiral CT uses an array of detectors composed of several independent detector modules, while the panel detector uses a one-piece scintillator of a large area with a large-scale array of light sensitive units, such as CCD, CMOS, TFT, etc., packaged at the back, where the X-ray intensity data is obtained after an analog to digital conversion. The progress of the panel detector technology brings out a new cone beam CT, i.e., CBCT. A CBCT system using the panel detector technology is capable of scanning a large region, such as 30 cm*30 cm, by rotating only one round and reconstructing a three-dimensional CT image within the field of view (FOV) of the scanning.
The CT technology also processes in the field of security inspection and industrial detection. For example, the CT used for security inspection which is based on the double energy mechanism is accepted and popularizes in the field of security inspection due to its good performance of differentiating substances. The industrial CT used in the industrial lossless detection field improves in respect to the spatial resolution, density resolution, etc.
It is also an important topic of research as how to accurately determine locations of interested objects (such as a metal object) during the process of CT image reconstruction.